bug#2439: 23.0.60; [patch] `Mark set' clobbers useful message in ibuffer

In ibuffer, running ibuffer-toggle-sorting-mode will produce a useful
message telling the user what the buffer is now sorted by. That
message is immediately clobbered by an useless `Mark set' message
(useless because ibuffer stomps all over any such mark).

To reproduce:

  emacs -Q
  M-x ibuffer
  ,
  C-h e and observe that both "Sorting by ..." and "Mark set" appear

A patch follows (against GNU Emacs 23.0.60.1 (i486-pc-linux-gnu, GTK+
Version 2.12.11) of 2008-11-22 on elegiac, modified by Debian).

diff -c -L /usr/share/emacs/23.0.60/lisp/ibuffer.el.gz -L
/tmp/buffer-content-31328m2 /tmp/jka-com3132uwF
/tmp/buffer-content-31328m2
*** /usr/share/emacs/23.0.60/lisp/ibuffer.el.gz
--- /tmp/buffer-content-31328m2
***************
*** 2277,2283 ****
        (setq buffer-read-only t)
        (set-buffer-modified-p ibuffer-did-modification)
        (setq ibuffer-did-modification nil)
!       (goto-line (1+ orig)))))

  (defun ibuffer-quit ()
    "Quit this `ibuffer' session.
--- 2277,2284 ----
        (setq buffer-read-only t)
        (set-buffer-modified-p ibuffer-did-modification)
        (setq ibuffer-did-modification nil)
!       (goto-char 1)
!       (forward-line orig))))

  (defun ibuffer-quit ()
    "Quit this `ibuffer' session.